I suspect there is a scenario where the taildir source can miss reading events from a log file due to how the source determines whether a file has been updated. In ReliableTaildirEventReader:
boolean updated = tf.getLastUpdated() < f.lastModified() ... tf.setNeedTail(updated);
Consider this sequence of events from TaildirSource.process(). Assume they all happen within the same second and there is just a single log file.
- Call ReliableTaildirEventReader.updateTailFiles()
- This call will set ReliableTaildirEventReader.updateTime to current time in milliseconds
- Assume the underlying file has not been updated within the last idleTimeout milliseconds
- Due to idleness, the tail file's inode is added to TaildirSource.idleInodes in idleFileCheckerRunnable
- tf.needTail is false. Skip reading file.
- Underlying file is updated with events E1
- Call TaildirSource.tailFileProcess() before close to read any pending events
- Events E1 are read and processed
- Since events were read, call ReliableTaildirEventReader.commit() which updates the tail file's position and sets its last updated time to ReliableTaildirEventReader.updateTime from 1.a
- Close file
- Events E2 are written to underlying file. File's modification time is in the same second as the tail file's last updated time.
- Since the time returned by File.lastModified() is the mtime in seconds converted to milliseconds the file's last modified time is less than the tail file's last updated time and taildir won't reopen the file to read E2.
- This behaviour of File.lastModified() may be platform/jvm specific. I confirmed the behavior using OpenJDK 8 on Ubuntu precise.
Can someone confirm this?